A direct methanol fuel cell (DMFC), like an ordinary battery, provides dc electricity from two electrochemical reactions. These reactions occur at electrodes to which reactants are continuously fed. The negative electrode (anode) is maintained by supplying a fuel such as methanol, whereas the positive electrode (cathode) is maintained by the supply of oxygen or air. When providing current, methanol is electrochemically oxidized at the anode electro-catalyst to produce electrons, which travel through the external circuit to the cathode electro-catalyst where they are consumed together with oxygen in a reduction reaction. The circuit is maintained within the cell by the conduction of protons in the electrolyte.
A direct methanol fuel cell system integrates a direct methanol fuel cell stack with different subsystems for instance for the management of water, fuel, air, humidification and thermal condition of the system. These subsystems are aimed to improve the overall efficiency of the system, which typically suffers from kinetic constraints within both electrode reactions together with the components of the cell stack. For instance, one issue with traditional DMFC systems relates to the separation of carbon dioxide from the anode exhaust stream. Carbon dioxide is typically separated prior to re-circulating the liquid mixture (methanol and water) back to the fuel cell stack inlet and is implemented by means of a gas/liquid separator system. In this traditional approach, the methanol and water vapor are first condensed by means of a cooling fan (or radiator) and the carbon dioxide gas thus separated from the liquid (methanol and water) is vented out. The recovered liquid methanol and water are then pumped by means of a re-circulating pump to a mixing tank where they are mixed with fresh methanol prior to being fed to the fuel cell stack. The fresh methanol is diluted with the recovered methanol and water to achieve a desired concentration prior to feeding it to the stack. The traditional process of separation of carbon dioxide from the methanol and water mixture is power consuming, requires bulky equipment and quite inefficient since some of the methanol and water present in a vapor form in the anode exhaust stream are lost along with the carbon dioxide. Accordingly, there is a need to develop new subsystems in particular related to carbon dioxide separation that could be integrated with a direct methanol fuel cell and system.